Radiation monitoring system and radiation monitoring method

Abstract

To provide a radiation monitoring system that can determine a critical margin of an object including nuclear fuel with partially unknown characteristics.SOLUTION: A radiation monitoring system is configured to include a gamma-ray detector for measuring gamma rays, a gamma-ray energy analysis device for analyzing gamma-ray energy from the output of the gamma-ray detector, a neutron detector for measuring neutrons, a neutron flux analysis device for analyzing neutron flux from the output of the neutron detector, an inverse multiplication analysis device for calculating inverse multiplication data based on a high-energy gamma-ray dose and an alternative gamma-ray dose acquired from the gamma-ray energy analysis device and a neutron flux acquired from the neutron flux analysis device, and an inverse multiplication curve processing device for calculating a critical margin from the high-energy gamma-ray dose and the inverse multiplication data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a radiation monitoring system and a radiation monitoring method. [Background technology]

[0002] Facilities that handle radioactive materials, including nuclear material, include nuclear power plants, nuclear fuel processing and fabrication facilities, accident reactors, waste disposal facilities, accelerator facilities, and facilities with controlled areas for radioactive materials. During the processing and use processes of objects containing nuclear fuel, the object may be damaged. Furthermore, depending on the damage, the object may become mixed with surrounding materials. When handling such objects whose properties are partially unclear, it is necessary to ensure safety while working to improve workability. To ensure safety, it is important to understand the criticality margin of partially unclear objects. Techniques for accurately monitoring the subcritical state of nuclear fuel material have been proposed for the purpose of grasping the criticality margin (see, for example, Patent Documents 1 and 2). In the technology described in Patent Document 1, the subcritical state of nuclear fuel material is accurately monitored from the gamma ray count rate and neutron count rate of the nuclear fuel material. In addition, in the technology described in Patent Document 2, the radioactivity ratio and neutron multiplication factor are calculated from the gamma rays and radioactivity concentration of collected fission product (FP) gas, and the subcritical state is monitored using an approximation formula that includes the measured neutron multiplication factor and the radioactivity ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6168582 [Patent Document 2] Patent No. 6110915 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 evaluates the weight of nuclear fuel material accumulated inside the strainer using the gamma-ray count rate of the Eu-154 peak. Furthermore, the criticality margin is estimated by extrapolating a predicted curve from a plot calculated using the neutron inverse multiplication method after multiple measurements. However, with the technology described in Patent Document 1, if the amount of water, neutron absorber, or even the amount of metal or ceramic contained in the measurement object is unclear, the inverse multiplication factor may change due to the influence of the material. In other words, the change in inverse multiplication factor may not simply correlate with the weight of the nuclear fuel material, i.e., the change in the gamma-ray count rate of the Eu-154 peak. For this reason, it is difficult to apply this method as a method for determining the criticality margin of an object containing nuclear fuel whose properties are partially unclear.

[0005] Furthermore, the technology described in Patent Document 2 remotely monitors the state of a measurement object by incorporating a step of aspirating gas in the space where the measurement object exists and collecting fission product gas contained in the gas. However, with the technology described in Patent Document 2, as the space where the measurement object exists becomes larger, the time required to aspirate gas from the space becomes longer, making it difficult to grasp the criticality margin at appropriate time intervals. Furthermore, when the space is large and the measurement object is spread over a wide area, the step of collecting fission product gas measures the average value of fission product gas present in the space. When the measurement object to be monitored is partial or localized, it is difficult to grasp the criticality margin of an object containing nuclear fuel whose properties are partially unclear.

[0006] In order to solve the above-mentioned problems, the present invention provides a radiation monitoring system and a radiation monitoring method that are capable of determining the criticality margin of an object containing nuclear fuel whose properties are partially unclear.

[0007] The above and other objects of the present invention and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0008] The radiation monitoring system of the present invention includes a gamma ray detector that measures gamma rays, a gamma ray energy analyzer that analyzes gamma ray energy from the output of the gamma ray detector, a neutron detector that measures neutrons, and a neutron flux analyzer that analyzes neutron flux from the output of the neutron detector.The system further includes an inverse multiplication analyzer that calculates inverse multiplication data based on the high-energy gamma ray dose and alternative gamma ray dose obtained from the gamma ray energy analyzer and the neutron flux obtained by the neutron flux analyzer, and an inverse multiplication curve processing device that calculates a critical margin from the high-energy gamma ray dose and the inverse multiplication data.

[0009] Furthermore, the radiation monitoring method of the present invention involves placing a gamma ray detector and a neutron detector near an object to be measured, measuring radiation with the gamma ray detector and the neutron detector, analyzing the high-energy gamma ray dose and inverse multiplication data, and calculating the critical margin from an inverse multiplication prediction curve based on the high-energy gamma ray dose and the inverse multiplication data. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a radiation monitoring system and a radiation monitoring method that are capable of determining the criticality margin of an object containing nuclear fuel whose properties are partially unclear.

[0011] Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a configuration diagram of a radiation monitoring system according to a first embodiment. [Figure 2] FIG. 2 is an output waveform diagram of a gamma ray detector. [Figure 3] 1 is a gamma ray energy spectrum output by a gamma ray energy analyzer. [Figure 4] FIG. 4 is a partially enlarged view of the gamma ray energy spectrum shown in FIG. 3. [Figure 5]FIG. 4 is an enlarged view of the high energy region in the gamma ray energy spectrum shown in FIG. 3. [Figure 6] This is a neutron spectrum formed by a neutron flux analyzer. [Figure 7] FIG. 1 is a diagram showing the relationship between the inverse multiplication factor (1 / M) and the high-energy gamma ray dose. [Figure 8] 1 is a flowchart of the operational steps of a radiation monitoring method. [Figure 9] FIG. 10 is a configuration diagram of a radiation monitoring system according to a second embodiment. [Figure 10] 1 is a flowchart of the operational steps of a radiation monitoring method. [Figure 11] FIG. 10 is a configuration diagram of a radiation monitoring system according to a third embodiment. [Figure 12] 1 is a diagram showing the relationship between the output tolerance of a gas management system output by a gas management system output conversion processing device and the amount of high-energy gamma rays S. [Figure 13] 1 is a flowchart of the operational steps of a radiation monitoring method. [Figure 14] FIG. 10 is a configuration diagram of a radiation monitoring system according to a fourth embodiment. [Figure 15] FIG. 10 is a configuration diagram of a radiation monitoring system according to a fifth embodiment. [Figure 16] 1 is a flowchart of the operational steps of a radiation monitoring method. [Figure 17] FIG. 10 is a configuration diagram of a radiation monitoring system according to a sixth embodiment. [Figure 18] 1 is a flowchart of the operational steps of a radiation monitoring method. [Figure 19] FIG. 13 is a configuration diagram of a radiation monitoring system according to a seventh embodiment. [Figure 20] FIG. 13 is a configuration diagram of a radiation monitoring system according to an eighth embodiment. [Figure 21] 1 is a diagram showing the relationship between the output (detector output D) from a gamma ray detector and a non-energy analysis type gamma dosimeter and the high-energy gamma ray dose S. DETAILED DESCRIPTION OF THE INVENTION

[0013] An example of a radiation monitoring system and a radiation monitoring method according to an embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following example. In each of the drawings described below, common components are given the same reference numerals. Furthermore, in the drawings used in this specification, identical or corresponding components are given the same reference numerals, and repeated explanations of these components may be omitted.

[0014] In facilities that handle radioactive materials, including nuclear materials, nuclear fuel materials such as uranium and plutonium are used for power generation and basic research. Facilities that handle nuclear fuel materials require safety management and accounting control of the nuclear fuel materials. For example, in nuclear power plants, radioactive materials, including nuclear materials, are usually stored underwater as fuel assemblies, and handling operations are carried out under strict safety management. When processing radioactive materials, including nuclear fuel, measures are taken to prevent the dispersion of radioactive materials and to mitigate the amount of dispersion, preventing the dispersion of scattered materials outside the system. Furthermore, when handling nuclear materials, remote operations are carried out while maintaining subcriticality. When handling radioactive materials, including nuclear materials, various operations within the facility must be carried out while ensuring sufficient safety. To improve the efficiency of various operations under such conditions, work processes and equipment that can be carried out while ensuring criticality safety are required.

[0015] 1. Radiation Monitoring System and Radiation Monitoring Method of First Embodiment A radiation monitoring system and a radiation monitoring method according to a first embodiment will be described. Figure 1 shows a configuration diagram of a radiation monitoring system according to a first embodiment. The radiation monitoring system 100 of Example 1 shown in Figure 1 is composed of a gamma ray detector 101, a gamma ray energy analyzer 102, a neutron detector 103, a neutron flux analyzer 104, an inverse multiplication analyzer 105, an inverse multiplication curve processor 106, and a display device 107. The gamma ray detector 101 and the neutron detector 103 are placed in a work area 109 in which a measurement object 108 containing radioactive material is present.

[0016] The radiation monitoring system 100 connects the gamma ray detector 101 to the gamma ray energy analysis device 102, thereby transmitting information regarding gamma ray detection to the gamma ray energy analysis device 102. Depending on the range of the measurement object 108 and the sensitivity of the gamma ray detector 101, multiple gamma ray detectors 101 are provided in the work area 109 and connected to the gamma ray energy analysis device 102. Similarly, the radiation monitoring system 100 connects the neutron detector 103 to the neutron flux analyzer 104, thereby transmitting information about neutron detection to the neutron flux analyzer 104. Depending on the range of the object to be measured and the sensitivity of the detector, multiple neutron detectors 103 may be provided in the work area 109 and connected to the neutron flux analyzer 104. The radiation monitoring system 100 connects the gamma ray energy analyzer 102 and the neutron flux analyzer 104 to the inverse multiplication analyzer 105, thereby transmitting radiation information required for calculating the inverse multiplication to the inverse multiplication analyzer 105. The radiation monitoring system 100 connects the inverse multiplication analysis device 105 to the inverse multiplication curve processing device 106, and transmits inverse multiplication data and operation and measurement timing data for constructing the inverse multiplication curve to the inverse multiplication curve processing device 106. In the radiation monitoring system 100, the demultiplication curve processing device 106 is connected to the display device 107, so that the operator 135 or the manager can check the processing results on the monitor of the display device 107 or on an interface such as a virtual space.

[0017] The measurement object 108 includes various types of materials, such as metals, ceramics, inorganic materials, and organic materials, in solid, liquid, or gas form. The radioactive materials included in the measurement object 108 include alpha ray sources, beta ray sources, gamma ray sources, and neutron sources. Examples of the radioactive materials included in the measurement object 108 include isotopes of uranium (U), plutonium (Pu), californium (Cm), americium (Am), neptunium (Np), strontium / yttrium (Sr / Y), cesium (Cs), europium (Eu), antimony (Sb), cerium (Ce), barium / lanthanum (Ba / La), zirconium / niobium (Zr / Nb), and ruthenium / rhodium (Ru / Rh).

[0018] In terms of radiation sources in the measurement object 108, examples include neutrons and gamma rays generated by spontaneous nuclear fission in the isotope itself, and neutrons, gamma rays, beta rays, alpha rays, etc. generated by induced nuclear reactions between the isotope and neutrons and protons present in the work area 109. In addition to the gamma ray detector 101, neutron detector 103, and measurement object 108, the work area 109 may contain work area structures such as piping, walls, floors, ceilings, and equipment, and substances similar to the measurement object 108 may exist on the surfaces or inside these work area structures.

[0019] The gamma ray detector 101 detects gamma rays originating from the measurement object 108 and outputs an electrical signal or an optical signal corresponding to the energy imparted to the gamma ray detector 101. Typical gamma ray detectors include, for example, semiconductor, scintillation, and optical fiber detectors. Semiconductor detectors include detectors using compound semiconductors such as silicon, silicon carbide (SiC), diamond, germanium (Ge), GaAs, CdTe, CZT, and TlBr. Scintillation detectors include detectors using various phosphors such as NaI, CsI, LaBr3, LaCl3, SrI, BGO, and GSO. Optical fiber detectors include detectors using YAG, YAP, and the phosphors used in the scintillation detectors described above attached to the tip of an optical fiber, and detectors using the optical fiber itself as a phosphor to analyze dose, energy, and position information.

[0020] Fig. 2 shows an output waveform diagram of the gamma ray detector 101. Fig. 2 shows, as an example of an output waveform, the output of a preamplifier in a gamma ray detector 101 equipped with a preamplifier inside. The gamma ray detector 101 outputs an electric pulse 110 that correlates with the energy imparted from gamma rays to a gamma ray sensor (not shown) provided inside the gamma ray detector 101. In general, the voltage value of the electric pulse 110 and its voltage integral correlate with the energy imparted to the gamma ray sensor.

[0021] The gamma ray energy analyzer 102 analyzes gamma ray energy based on an output signal such as the electrical pulse 110 output from the gamma ray detector 101, and outputs the gamma ray energy for each gamma ray detected. 3 shows a gamma-ray energy spectrum output by the gamma-ray energy analyzer 102. The gamma-ray energy analyzer 102 forms a gamma-ray energy spectrum 111 using the acquired gamma-ray energy information. As an example, a Cs-137-derived gamma-ray peak 112 (662 keV), a Cs-134-derived gamma-ray peak 113 (796 keV), Eu-154-derived gamma-ray peaks 114 and 115 (1274 keV and 1596 keV), and a continuous distribution 116 resulting from high-energy gamma rays resulting from induced nuclear fission of uranium or the like contained in the measurement object 108 are shown. Here, a continuous distribution is a region without peaks in the spectrum, and is a spectral distribution that is arbitrarily set by the administrator of the radiation monitoring system 100 or the like.

[0022] The gamma ray energy analyzer 102 transmits to the downstream inverse multiplication analyzer 105 alternative gamma ray quantities from alternative gamma ray sources, which substitute for the intensity of an external neutron source normally used in the calculation of inverse multiplication, as described below. Furthermore, the gamma ray energy analyzer 102 transmits high-energy gamma ray quantities from gamma rays in a higher energy range than the gamma ray energy (2.2 MeV) generated by the nuclear reaction of hydrogen and neutrons. Examples of alternative gamma ray sources include Eu-154, Cs-137, Cs-134, Sb-125, Ce-144, Ba140 / La-140, Zr-95 / Nb-95, and Ru-106 / Rh106. The gamma ray energy analyzer 102 detects and analyzes gamma ray peaks resulting from one or more of these alternative gamma ray sources.

[0023] Fig. 4 shows an enlarged view of a portion of the gamma-ray energy spectrum shown in Fig. 3. For example, when a gamma-ray source derived from Eu-154 is used as the alternative gamma-ray source, the gamma-ray energy analyzer 102 analyzes the peak intensity (count value) 117 of the gamma-ray peak 114 derived from Eu-154 and regards it as the alternative gamma-ray dose.

[0024] 5 shows an enlarged view of the high-energy region in the gamma-ray energy spectrum shown in FIG. 3. In order to analyze the amount of high-energy gamma rays, the gamma-ray energy analyzer 102 sets, for example, a region of interest 118, analyzes the intensity (count value) 119 of the gamma-ray spectrum within the region of interest 118, and regards it as the amount of high-energy gamma rays. Note that the region of interest 118 has a lower (low-energy) threshold set to a value higher than the gamma-ray energy (2.2 MeV) generated by the nuclear reaction of hydrogen and neutrons. The upper and lower threshold values ​​of the region of interest 118 are set arbitrarily by the administrator of the radiation monitoring system 100, etc.

[0025] The neutron detector 103 detects neutrons originating from the measurement object 108 and outputs an electrical signal or an optical signal corresponding to the energy imparted to the neutron detector 103 . When measuring neutrons, the neutron detector 103 may be either a detector that measures thermal neutrons or epithermal neutrons, or a fast neutron detector that measures fast neutrons, or both.

[0026] Typical types of thermal neutron detectors include gas detectors, scintillation detectors, and semiconductor detectors, which use thermal neutron sensitive materials such as lithium, boron, gadolinium, cadmium, uranium, and plutonium. Gas detectors that can be used include He-3 proportional counters, BF3 proportional counters, B-10 coated proportional counters, and fission counters. Scintillation detectors are equipped with scintillators containing elements with a large cross section for thermal neutrons, such as lithium-6, boron-10, and gadolinium. Types of scintillators include, for example, LiI:Eu, ZnS:Ag, plastic scintillators containing boron-10, glass scintillators containing lithium-6 or boron-10, LiCaAlF6, and Gd3Al2Ga3O. 12, Gd2SiO5:Ce, Cs2LiLaBr6:Ce, Cs2LiYCl6:Ce, Cs2LiLaCl6:Ce, Cs2LiLaBr6-xClx:Ce, and Cs2LiYBr6:Ce. Another method involves coating the surface of the scintillator with an element that is sensitive to thermal neutrons. In this case, not only the scintillators mentioned above, but also all scintillators used as radiation detectors, such as LaBr3, CsBr3, LYSO, LSO, GAGG, CsI, NaI, BGO, GPS, La-GPS, LuAG, SrI, and plastic scintillators, can be used as neutron detectors. Similarly, semiconductor detectors are equipped with semiconductors containing elements with a large cross section for thermal neutrons, such as lithium-6, boron-10, and gadolinium. Examples of semiconductors that can be used include CdTe and CdZnTe. Another method involves coating the surface of the semiconductor with an element that is sensitive to thermal neutrons. In this case, semiconductor detectors can be used not only with CdTe and CdZnTe, but also with silicon, germanium, diamond, silicon carbide, and semiconductor detectors with perovskite structures such as CsPbCl3, CsPbBr3, and LiTaO3.

[0027] Epithermal neutron detectors include gas detectors such as recoil proton counters, which use hydrogen gas or methane gas as the sensitive element and measure the energy imparted by recoil protons resulting from the reaction between neutrons and hydrogen. Threshold detectors are used for fast neutron detectors. One of the main types of threshold detectors is the fission counter, which uses uranium-234, uranium-236, uranium-238, neptunium-237, thorium-232, etc. as the neutron-sensitive element. Fast neutron detectors also use organic scintillators such as anthracene and stilbene. Furthermore, fast neutron detectors can also be used that measure fast neutrons using the scintillation light emitted from pressurized helium-4 gas.

[0028] When the neutron detector 103 has an internal preamplifier, it outputs a signal similar to the output waveform diagram shown in Fig. 2, just like the gamma ray detector 101. The neutron detector 103 analyzes the energy caused by neutrons from the voltage value and voltage integral value of the electric pulse, which correlate with the energy released based on the nuclear reaction that occurs inside, and counts the signals caused by neutrons.

[0029] The neutron flux analyzer 104 forms a neutron spectrum using neutron detection information acquired from the neutron detector 103. FIG. 6 shows a neutron spectrum 120 formed by the neutron flux analyzer 104. As an example of a neutron spectrum, FIG. 6 shows an example of a neutron spectrum obtained when a B-10 coated proportional counter is used. In the neutron spectrum shown in FIG. 6, a continuous distribution 121 is formed by energy signals resulting from the nuclear reaction between boron-10 and thermal neutrons. When gamma rays are present in the working area 109, a continuous distribution 122 resulting from the gamma rays is formed in a region of low applied energy, depending on the sensitivity of the neutron detector 103. To analyze the neutron flux from this neutron spectrum 120, for example, a region of interest 123 is set. Then, the intensity (count value) 124 of the neutron spectrum inside the region of interest 123 is analyzed, and the neutron flux is calculated using a neutron count value-neutron flux conversion coefficient prepared in advance. The upper and lower threshold values ​​of the region of interest 123 are arbitrarily set by the administrator of the radiation monitoring system 100, etc.

[0030] The demultiplication analyzer 105 calculates the demultiplication data using the following equation (1).

[0031]

number

[0032] In the above equation (1), M is the multiplication of neutrons due to induced fission, C0 is the neutron flux in the initial state of the operation, and C n is the neutron flux in the working n state, S0 is the intensity of the alternative gamma ray source for the external neutron source in the initial working state, S nis the strength of the alternative gamma ray source for the external neutron source in the working n state, k0 is the neutron multiplication factor in the initial working state, and k eff is the neutron multiplication factor.

[0033] In the above equation (1), the neutron flux C0 in the initial state of work and the neutron flux C n The neutron flux obtained by the neutron flux analyzer 104 is substituted for the intensity S of the alternative gamma ray source for the external neutron source in the initial state of the operation. 0、 and the strength S of the alternative gamma ray source for the external neutron source in the working n state n is substituted with the surrogate gamma ray dose obtained by the gamma ray energy analyzer 102. If the initial neutron multiplication factor k0 is known, that value is substituted, and if it is unknown, 0 is substituted. By calculating the inverse multiplication data using equation (1), it is possible to perform a relative evaluation of the inverse multiplication factor (1 / M).

[0034] FIG. 7 shows a relationship diagram between the inverse multiplication factor (1 / M) and the high-energy gamma ray dose S. The inverse multiplication curve processing device 106 outputs a relationship diagram 125 between the inverse multiplication factor and the high-energy gamma ray dose using the inverse multiplication factor data (1 / M) obtained by the inverse multiplication factor analyzer 105 and the high-energy gamma ray dose S at the time of obtaining the inverse multiplication factor data. As examples, FIG. 7 shows an inverse multiplication factor-high-energy gamma ray dose plot 126 for the initial state, an inverse multiplication factor-high-energy gamma ray dose plot 127 for working state n, and an inverse multiplication factor-high-energy gamma ray dose plot 128 for working state n+1. The inverse multiplication factor curve processing device 106 uses the plots 126, 127, and 128 to calculate an inverse multiplication prediction curve 129 using a fitting function configured from an arbitrarily set linear function, quadratic function, exponential function, etc., and a general fitting method such as the least squares method. FIG. 7 shows an example of an inverse multiplication predicted curve calculated by the inverse multiplication curve processor 106, which is fitted with a linear function.

[0035] The inverse multiplication curve processing device 106 calculates the point of contact (1 / M→0) between the inverse multiplication prediction curve 129 and the horizontal axis as a critical prediction point 130. Furthermore, when the latest work state is work state n+1, the inverse multiplication curve processing device 106 calculates the high-energy gamma ray dose S n+1 and the latest predicted critical point 130. Then, the inverse multiplication curve processor 106 calculates and obtains the difference between the latest high-energy gamma ray dose S n+1 and the latest critical prediction point 130 (ΔS n+1 ) is obtained as the critical margin 131 in the working state n+1.

[0036] In the radiation monitoring system described above, the display device 107 displays inputs and outputs on a monitor or in a virtual space for the workers, their managers, and other related parties. The display device 107 can also display the various diagrams shown in the above embodiments and video data of the work area superimposed on them.

[0037] [Radiation monitoring method flowchart] Next, a description will be given of a radiation monitoring method using the above-described radiation monitoring system 100. Fig. 8 shows a flowchart of the work steps of the radiation monitoring method using the above-described radiation monitoring system 100. First, the gamma ray detector 101 and the neutron detector 103 are placed near the object to be measured (step S101). Next, each radiation is measured, and the inverse multiplication rate and the amount of high-energy gamma rays are analyzed (step S102). In this step, the radiation monitoring system 100 first acquires information about gamma ray detection in the measurement object 108 from the gamma ray detector 101, and information about neutron detection from the neutron detector 103. Then, the gamma ray energy analyzer 102 analyzes the gamma ray energy in the measurement object 108 based on the information about gamma ray detection acquired by the gamma ray detector 101, and outputs the intensity of the alternative gamma ray source and the amount of high-energy gamma rays for each gamma ray detection. Furthermore, the neutron flux analyzer 104 outputs neutron flux based on the neutron detection information acquired from the neutron detector 103. Then, the inverse multiplication analysis device 105 calculates inverse multiplication data using the intensity of the alternative gamma ray source calculated by the gamma ray energy analysis device 102, the neutron flux calculated by the neutron flux analysis device 104, and the above-mentioned equation (1).

[0038] Next, the high-energy gamma ray dose at which the inverse multiplication becomes zero is estimated from the inverse multiplication prediction curve of the high-energy gamma ray dose and the inverse multiplication (step S103). In this step, the inverse multiplication curve processing device 106 calculates an inverse multiplication prediction curve that shows the relationship between the inverse multiplication and the high-energy gamma ray dose based on the calculated inverse multiplication data. Then, the inverse multiplication curve processing device 106 estimates the high-energy gamma ray dose at which the inverse multiplication (1 / M) becomes zero based on the calculated inverse multiplication prediction curve. Next, the critical margin is calculated (step S104). In this step, the inverse multiplication curve processor 106 calculates the latest high-energy gamma ray dose S n+1 The difference between the latest predicted critical point and the latest predicted critical point is calculated as the critical margin in the working state n+1.

[0039] Next, the manager or the like determines changes in the measurement object and the work environment in which the measurement object is present (step S105). The manager or the like determines changes in the work environment, for example, changes in the shape of the work location based on images from a camera installed in the work area 109, changes in data such as radiation doses from each detector, etc. Alternatively, the manager or the like may quantify the amount of change in the work environment on behalf of the manager, and make a determination based on a threshold value using a computing device.

[0040] If there is a change (Yes in step S105), a decision is made to change the measurement position (step S107). In this step, the manager or the like decides whether the gamma ray detector 101 and the neutron detector 103 placed near the object to be measured in step S101 are in an appropriate position for detecting radiation at the work position. If the positions are not appropriate for detecting radiation due to a change in the work environment, the manager or the like decides to change the measurement position. If there is a change in the measurement position (Yes in step S107), the process returns to step S101. If there is no change in the measurement position (No in step S107), the process returns to step S102.

[0041] If there is no change (No in step S105), it is determined whether the work is complete (step S106). If the work is not complete (No in step S106), the process returns to the start after waiting as necessary (step S108). If the work is completed (Yes in step S106), the process according to this flowchart ends.

[0042] By using the radiation monitoring system and radiation monitoring method described above, it is possible to grasp the criticality margin even for an object containing nuclear fuel whose properties are partially unclear. Therefore, when handling an object whose properties are partially unclear, it is possible to improve workability while ensuring safety.

[0043] 2. Radiation Monitoring System and Radiation Monitoring Method of Second Embodiment Next, a radiation monitoring system and a radiation monitoring method according to a second embodiment will be described. The radiation monitoring system and the radiation monitoring method according to the second embodiment use a control threshold for high-energy gamma ray dose to determine whether work is permitted in a work area. The radiation monitoring system and the radiation monitoring method according to the second embodiment differ from the radiation monitoring system and the radiation monitoring method according to the first embodiment described above only in the configuration related to the determination process using the control threshold. Therefore, the following description will focus on the configuration related to the determination process using the control threshold, and detailed description of the configuration similar to that of the first embodiment described above will be omitted.

[0044] A configuration diagram of a radiation monitoring system according to the second embodiment is shown in Fig. 9. The radiation monitoring system 200 shown in Fig. 9 is configured by adding a work feasibility processing device 132, an inter-worker communication device 133, a neutron absorbing material injection system 134, and a neutron transport duct 136 to the radiation monitoring system 100 shown in the first embodiment.

[0045] The work propriety processing device 132 monitors whether the criticality margin 131 obtained by the inverse multiplication curve processing device 106 exceeds the control threshold for the amount of high-energy gamma rays. The control threshold is stored, for example, in a memory unit or the like of the radiation monitoring system 200. The control threshold may be set by a manager or the like, or may be a value determined by operational rules applied in the work environment or by relevant laws and regulations.

[0046] The inter-worker communication device 133 is configured by a general communication device. The inter-worker communication device 133 is connected to multiple workers 135 so that various data can be sent and received between the workers and information devices (for example, mobile communication devices). When the amount of high-energy gamma rays exceeds the management threshold, the worker 135 monitoring the display device 107 quickly contacts the other workers 135 using the inter-worker communication device 133.

[0047] The neutron absorbing material injection system 134 has a container that stores neutron absorbing material, and a neutron transfer duct 136 that connects the container to the work area 109. A sufficient amount of neutron absorbing material is stored in the container of the neutron absorbing material injection system 134 in advance. Then, the neutron absorbing material injection system 134 is operated by an operator 135 to spray the neutron absorbing material into the work area 109 through the neutron transfer duct 136.

[0048] [Radiation monitoring method flowchart] Next, a description will be given of a radiation monitoring method using the above-described radiation monitoring system 200. Fig. 10 shows a flowchart of the work steps of the radiation monitoring method using the above-described radiation monitoring system 200.

[0049] First, similarly to the first embodiment, the steps from arranging the gamma ray detector 101 and the neutron detector 103 (step S101) to calculating the criticality margin (step S104) are carried out. Next, the work possibility processing device 132 determines whether the control threshold is exceeded (step S201). In this step, the work possibility processing device 132 determines whether the critical margin (ΔSn+1 ) exceeds a predetermined control threshold. If the control threshold is exceeded (Yes in step S201), the neutron absorbing material injection system 134 injects neutron absorbing material according to the operation of the operator 135 (step S202). In this step, the work feasibility processing device 132 outputs information that the criticality margin has exceeded the control threshold to the display device 107. The operator 135 monitoring the display device 107 uses the inter-operator communication device 133 to contact the operator 135 who is capable of operating the neutron absorbing material injection system 134. Then, the operator 135 who is capable of operating the neutron absorbing material injection system 134 operates the neutron absorbing material injection system 134, and injects neutron absorbing material from the neutron absorbing material injection system 134 into the work area 109. If the control threshold is not exceeded (No in step S201), a determination is made as to whether there has been a change in the measurement object and the work environment in which the measurement object exists (step S105). After that, the same operations as in the first embodiment are carried out.

[0050] By using the above-described radiation monitoring system and radiation monitoring method, it is possible to grasp the criticality margin even for an object containing nuclear fuel whose properties are partially unclear. Furthermore, based on the grasped criticality margin and control threshold, it is possible to determine the safety of the work area 109, and to quickly ensure safety and carry out work even when the risk increases. Therefore, when handling an object whose properties are partially unclear, it is possible to improve workability while ensuring safety.

[0051] 3. Radiation Monitoring System and Radiation Monitoring Method of Third Embodiment Next, a radiation monitoring system and a radiation monitoring method of a third embodiment will be described. The radiation monitoring system and the radiation monitoring method of the third embodiment determine whether work can be performed in a work area using the output value of the gas management system when the demultiplication rate approaches 0. The radiation monitoring system and the radiation monitoring method of the third embodiment differ from the radiation monitoring system and the radiation monitoring method of the second embodiment described above only in the configuration related to the gas management system. Therefore, the configuration related to the gas management system will be described below, and detailed descriptions of the configuration similar to those of the first and second embodiments will be omitted.

[0052] A configuration diagram of a radiation monitoring system according to the third embodiment is shown in Fig. 11. The radiation monitoring system 300 shown in Fig. 11 includes the radiation monitoring system 200 shown in the second embodiment, as well as a gas recovery duct 137, a gas management system 138, a gas management system output conversion processing device 139, and a work feasibility processing device 140.

[0053] The gas management system 138 collects gas in the space within the work area 109 through the gas collection duct 137 and measures the radioactivity concentration in the gas. The radioactive nuclides measured by the gas management system 138 are gaseous fission products produced by induced nuclear fission, such as xenon (Xe), krypton (Kr), and iodine (I).

[0054] The gas management system output conversion processing device 139 calculates the output margin from the high-energy gamma ray dose S and critical margin 131 obtained from the inverse multiplication curve processing device 106 and the radioactivity concentration in the gas obtained by the gas management system 138. Fig. 12 shows a relationship diagram between the output margin of the gas management system 138 and the high-energy gamma ray dose S, output by the gas management system output conversion processing device 139. In Fig. 12, the horizontal axis represents the high-energy gamma ray dose S, the same as in Fig. 7, and the critical margin 131 is also shown in the same way. The gas management system output conversion processing device 139 outputs a relationship diagram between the high-energy gamma ray dose S and the radioactivity concentration in the gas.

[0055] As an example, Figure 12 shows the ratio of the high-energy gamma ray dose S to the radioactivity concentration in the gas as a linear expression. Depending on the environment and system configuration, the relationship between the high-energy gamma ray dose S and the radioactivity concentration in the gas can also be expressed as a polynomial, exponential function, or the like. As shown in Figure 12, using the relationship between the high-energy gamma ray dose S and the radioactivity concentration in the gas, the gas management system output conversion processing device 139 calculates the critical margin 155 of the radioactivity concentration in the gas at which the inverse multiplication factor (1 / M) becomes 0 from the critical margin 131 of the high-energy gamma ray dose S.

[0056] The work feasibility processing device 140 monitors whether the criticality margin 155 of the gas control system 138 obtained by the gas control system output conversion processing device 139 exceeds the control threshold of the gas control system. The control threshold of the gas control system is also stored in, for example, a memory unit of the radiation monitoring system 300.

[0057] [Radiation monitoring method flowchart] Next, a description will be given of a radiation monitoring method using the above-described radiation monitoring system 300. Fig. 13 shows a flowchart of the work steps of the radiation monitoring method using the above-described radiation monitoring system 300.

[0058] First, similarly to the first embodiment, the steps from arranging the gamma ray detector 101 and the neutron detector 103 (step S101) to calculating the criticality margin (step S104) are carried out. Next, the gas management system output conversion processing device 139 calculates the output of the gas management system 138 corresponding to the high-energy gamma ray dose S at which the inverse multiplication rate becomes 0 (step S301). In this step, the gas management system output conversion processing device 139 calculates a relational expression of the high-energy gamma ray dose S - the radioactivity concentration in the gas from the high-energy gamma ray dose acquired from the inverse multiplication curve processing device 106 and the radioactivity concentration in the gas acquired from the gas management system 138. Then, the gas management system output conversion processing device 139 calculates, from the calculated relational expression, the critical margin 155 of the radioactivity concentration in the gas at which the inverse multiplication rate becomes 0, which corresponds to the critical margin 131 of the high-energy gamma ray dose.

[0059] Next, the work propriety processing device 132 determines whether the control threshold is exceeded (step S302). In this step, the work propriety processing device 132 determines whether the critical margin 155 of the radioactivity concentration in the gas calculated by the gas management system output conversion processing device 139 exceeds a predetermined control threshold. If the control threshold is exceeded (Yes in step S302), the neutron absorbing material injection system 134 injects the neutron absorbing material (step S302) in accordance with the operation of the operator 135. This step is performed in the same manner as step S202 in the second embodiment described above. If the control threshold is not exceeded (No in step S301), a determination is made as to whether there has been a change in the measurement object and the work environment in which the measurement object exists (step S105). After that, the same operations as in the first embodiment are carried out.

[0060] By using the above radiation monitoring system and radiation monitoring method, it is possible to grasp the criticality margin even for objects containing nuclear fuel whose properties are partially unclear. Furthermore, not only the high-energy gamma ray dose but also the criticality margin 155 of the radioactivity concentration in the gas is calculated, and the safety of the work area 109 is determined based on the criticality margin 155 and the control threshold. This makes it possible to detect conditions that increase risk more accurately and quickly ensure safety while carrying out work.

[0061] 4. Radiation Monitoring System and Radiation Monitoring Method of Fourth Embodiment Next, a radiation monitoring system and a radiation monitoring method according to a fourth embodiment will be described. The radiation monitoring system and the radiation monitoring method according to the fourth embodiment include a remote access device equipped with a gamma ray detector and a neutron detector. The radiation monitoring system and the radiation monitoring method according to the fourth embodiment differ from the radiation monitoring system and the radiation monitoring method according to the first embodiment described above only in the configuration related to the remote access device. Therefore, the configuration related to the remote access device will be described below, and detailed descriptions of the configurations similar to those of the first and second embodiments will be omitted. Furthermore, the fourth embodiment can apply the same operational steps as those of the first embodiment described above. Therefore, descriptions of the operational steps of the radiation monitoring method using a flowchart will be omitted.

[0062] A configuration diagram of a radiation monitoring system according to the fourth embodiment is shown in Fig. 14. The radiation monitoring system 400 shown in Fig. 14 is configured by adding remote access devices 141 and 142 and a remote access control system 143 to the radiation monitoring system 100 shown in the first embodiment.

[0063] The remote access devices 141, 142 are equipped with a gamma ray detector 101 and a neutron detector 103, and are remotely operated to operate within the work area 109. In FIG. 14, as examples of the remote access devices 141, 142, the remote access device 141 is shown as a manipulator type and the remote access device 142 is shown as a crawler type. The remote access devices 141, 142 are not limited to this, and other forms may be used. Also, in FIG. 14, multiple types of remote access devices 141, 142 are each equipped with a gamma ray detector 101 and a neutron detector 103, but a configuration in which both the gamma ray detector 101 and the neutron detector 103 are equipped in a single remote access device is also possible. Furthermore, the remote access devices 141, 142 may be equipped with an optical camera or a rangefinder to acquire information about the measurement object 108 and the work area 109.

[0064] The remote access control system 143 remotely controls and operates the remote access devices 141, 142 based on the decision-making of the worker 135. The remote access control system 143 has an internal control algorithm and is equipped with the function of automatically and autonomously controlling the manipulator and crawler. The remote access control system 143 can also support the operation by the worker 135 using the control algorithm. The worker 135 also acquires various information using the optical cameras and rangefinders equipped in the remote access devices 141, 142, judges the site situation based on the acquired information, and makes decisions regarding the operation of the remote access devices 141, 142, etc. By using the above-described radiation monitoring system and radiation monitoring method, even if the range of the measurement object 108 is wide, it is possible to move to the location where measurement is required and measure radiation using the remote access devices 141, 142 and the remote access control system 143. Therefore, even if the risk increases in a larger work area 109, it is possible to carry out work quickly while ensuring safety.

[0065] 5. Radiation Monitoring System and Radiation Monitoring Method of Fifth Embodiment Next, a radiation monitoring system and a radiation monitoring method of a fifth embodiment will be described. Note that the radiation monitoring system and the radiation monitoring method of the fifth embodiment differ from the radiation monitoring system and the radiation monitoring method of the first embodiment described above only in the configuration in which operation is continued within a range in which the high-energy gamma ray dose and the control threshold value determined by the output of the gas management system are not exceeded. Therefore, detailed description of the configuration similar to that of the first and second embodiments described above will be omitted below.

[0066] A configuration diagram of a radiation monitoring system according to the fifth embodiment is shown in Fig. 15. The radiation monitoring system 500 shown in Fig. 15 includes a remote-operated device 144 and a remote-operated control system 145 in addition to the radiation monitoring systems 200, 300, and 400 shown in the second to fourth embodiments.

[0067] The remote-operated work device 144 is placed inside the work area 109 and performs a predetermined task on the measurement target 108 and structures surrounding the work area 109. While a crawler-type remote-operated work device is shown in FIG. 15 as an example of the remote-operated work device 144, the remote-operated work device 144 is not limited to this. The remote-operated work device 144 is equipped with a work tool for performing the predetermined task. The work tool is, for example, a tool or equipment such as a core boring tool, a saw, a cutter, a chisel, a pump, a suction jig, and a gripper.

[0068] The remote work control system 145 remotely controls and operates the remote work device 144 based on the decision-making of the worker 135. The remote work control system 145 has an internal control algorithm and is equipped with the function of automatically or autonomously controlling the manipulator, crawler, work tool, etc. The remote work control system 145 can also support the operation by the worker 135 using the control algorithm. The worker 135 also acquires information from the optical camera and rangefinder equipped on the remote work device 144, judges the site situation based on the acquired information, and makes decisions on the operation of the remote work device 144, etc.

[0069] [Radiation monitoring method flowchart] Next, a description will be given of a radiation monitoring method using the above-described radiation monitoring system 500. Fig. 16 shows a flowchart of the work steps of the radiation monitoring method using the above-described radiation monitoring system 500.

[0070] First, similar to the first embodiment, the process from arranging the gamma ray detector 101 and the neutron detector 103 (step S101) to calculating the criticality margin (step S104) is performed. Furthermore, similar to the second embodiment, the process from determining whether the control threshold is exceeded (step S201) to introducing neutron absorbing material (step S202) is performed.

[0071] Next, the worker or manager determines whether the work is complete (step S401). If the work is not completed (No in step S401), the manager calculates the amount of work that can be done (step S402). Next, the worker or manager performs the work while adjusting the amount of work within the range of the possible amount of work (step S403). For example, the worker operates the remote-operated device 144 in the work area 109 using the remote operation control system 145 to perform the predetermined work. Next, changes in the measurement object 108 and the work environment in which the measurement object 108 exists are confirmed (step S404). Next, it is determined whether the measurement position has been changed (step S107). If the measurement position has been changed (Yes in step S107), the process returns to step S101. If the measurement position has not been changed (No in step S107), the process returns to step S102. If the work is completed (Yes in step S401), the process according to this flowchart ends.

[0072] By using the above radiation monitoring system and radiation monitoring method, it is possible to grasp the criticality margin even for objects containing nuclear fuel whose properties are partially unclear. Furthermore, even if the danger in the work area increases, it is possible to quickly ensure safety and proceed with work within the scope of ensuring safety. This makes it possible to plan and promote work that is optimal for the work situation.

[0073] 6. Radiation Monitoring System and Radiation Monitoring Method of Sixth Embodiment Next, a radiation monitoring system and a radiation monitoring method according to a sixth embodiment will be described. Note that the radiation monitoring system and the radiation monitoring method according to the sixth embodiment differ from the fifth embodiment only in that they include a step of adjusting the placement of workers and work equipment, the work process, and the work plan according to the amount of work adjustment in order to carry out work while ensuring safety. Therefore, detailed descriptions of the same configuration as the fifth embodiment will be omitted below.

[0074] A configuration diagram of a radiation monitoring system according to the sixth embodiment is shown in Fig. 17. The radiation monitoring system 600 shown in Fig. 17 includes a work plan updating system 146 in addition to the radiation monitoring system 500 shown in the fifth embodiment.

[0075] The work plan update system 146 updates the work process, work plan, and the allocation of workers and work equipment based on the available work volume, adjusted work volume, and work process volume. Furthermore, when the criticality margin is updated as the work progresses, the work process, work plan, and allocation of workers and work equipment are updated based on the updated data. This updating is performed by an automatic calculation method using a mathematical algorithm such as mathematical programming, or manually by the worker 135, and the decision is made by the work manager 147.

[0076] [Radiation monitoring method flowchart] Next, a description will be given of a radiation monitoring method using the above-described radiation monitoring system 600. Fig. 18 shows a flowchart of the work steps of the radiation monitoring method using the above-described radiation monitoring system 600.

[0077] First, as in the first embodiment, the process is carried out from arranging the gamma ray detector 101 and the neutron detector 103 (step S101) to calculating the criticality margin (step S104). Then, as in the second embodiment, the process is carried out from determining whether the control threshold has been exceeded (step S201) to introducing neutron absorbing material (step S202). Furthermore, as in the fifth embodiment, the process is carried out from determining whether the work is complete (step S401) to calculating the amount of work that can be done (step S402).

[0078] Next, the work manager 147 updates the work process, work plan, and worker / work device allocation based on the available work volume, work adjustment volume, and work process volume in the work plan update system 146 (step S501). Next, the work manager 147 and the worker 135 carry out the work while adjusting the amount of work within the range of the possible amount of work (step S502). Next, changes in the measurement object 108 and the work environment in which the measurement object 108 exists are confirmed (step S503). Next, the work manager 147 determines whether or not the plan needs to be updated (step S504). If an update is required (Yes in step S504), the process returns to step S501. If updating is not required (No in step S504), it is determined whether the measurement position has been changed (step S107). If the measurement position has been changed (Yes in step S107), the process returns to step S101. If the measurement position has not been changed (No in step S107), the process returns to step S102. If the work is completed (Yes in step S401), the process according to this flowchart ends.

[0079] By using the above radiation monitoring system and radiation monitoring method, even if the danger in the work area increases, safety can be ensured quickly and work can proceed within the scope of ensuring safety. This makes it possible to plan and promote work that is optimal for the work situation.

[0080] 7. Radiation Monitoring System and Radiation Monitoring Method of Seventh Embodiment Next, a radiation monitoring system and a radiation monitoring method according to a seventh embodiment will be described. The radiation monitoring system and the radiation monitoring method according to the seventh embodiment differ from the first embodiment described above only in that they include a step of estimating the amount of the object to be measured at which the reverse multiplication becomes zero by utilizing the analysis of the object to be measured and the analysis results. Therefore, detailed description of the same configuration as in the first embodiment described above will be omitted below. Furthermore, the seventh embodiment can apply the same operational steps as in the first embodiment described above. Therefore, a description of the operational steps of the radiation monitoring method using a flowchart will be omitted.

[0081] A configuration diagram of a radiation monitoring system according to the seventh embodiment is shown in Fig. 19. The radiation monitoring system 700 shown in Fig. 19 includes a measurement object database 148, a high-energy gamma ray dose prediction device 149, and a demultiplication curve processing device 150, in addition to the radiation monitoring system 100 shown in the first embodiment.

[0082] The measurement object database 148 is a database that stores the analysis results for the measurement objects and the analytical results. This database is stored in the storage unit of the radiation monitoring system 700, for example.

[0083] The high-energy gamma ray dose prediction device 149 sets the composition of the measurement object 108 based on various results stored in the measurement object database 148. Examples of the measurement object 108 include concrete, silicon, metal, ceramic, and resin in the work area 109. The high-energy gamma ray dose prediction device 149 calculates the high-energy gamma ray dose associated with changes in the material quantity of the measurement object 108 based on the set composition. The high-energy gamma ray dose prediction device 149 also displays the calculation results on the display device 107.

[0084] The inverse multiplication curve processing device 150 incorporates the predicted value of the high-energy gamma ray dose associated with the change in substance quantity calculated by the high-energy gamma ray dose prediction device 149 into the function of the inverse multiplication curve processing device 106 of the radiation monitoring system 100 of the first embodiment. The inverse multiplication curve processing device 150 also estimates the substance quantity of the measurement object at which the inverse multiplication becomes 0. The inverse multiplication curve processing device 150 also displays the processing results to the operator 135 via the display device 107.

[0085] By using the above radiation monitoring system and radiation monitoring method, it is possible to grasp the criticality margin even for objects containing nuclear fuel whose properties are partially unclear. Furthermore, it is possible to predict the amount of high-energy gamma rays that will be emitted in response to changes in the quantity of the object being measured, thereby supporting decision-making in work management by workers.

[0086] 8. Radiation Monitoring System and Radiation Monitoring Method of Eighth Embodiment Next, a radiation monitoring system and a radiation monitoring method according to an eighth embodiment will be described. The radiation monitoring system and the radiation monitoring method according to the eighth embodiment differ from the first embodiment only in that they include a non-energy analysis type gamma dosimeter that can operate even at high gamma radiation doses. Therefore, detailed descriptions of the same configuration as in the first embodiment will be omitted below. Furthermore, the eighth embodiment can apply the same operational steps as in the first embodiment. Therefore, descriptions of the operational steps of the radiation monitoring method using a flowchart will be omitted.

[0087] A configuration diagram of a radiation monitoring system according to the eighth embodiment is shown in Fig. 20. The radiation monitoring system 800 shown in Fig. 20 includes the radiation monitoring system 100 shown in the first embodiment, as well as a non-energy analysis type gamma dosimeter 151, a high-energy gamma ray dose analyzer 152, and an inverse multiplication analyzer 153.

[0088] The non-energy analysis type gamma dosimeter 151 is applicable not only to semiconductor detectors and scintillation detectors shown in the radiation monitoring system 100 of the first embodiment, but also to gas detectors. Gas detectors are, for example, ionization chambers, proportional counters, and GM counters. The radiation monitoring system 800 is provided with a non-energy analysis type gamma dosimeter 151 in parallel with the gamma ray detector 101 and neutron detector 103 in the work area 109. The non-energy analysis type gamma dosimeter 151 is used when the atmospheric dose rate in the work area 109 becomes so high that the output of the gamma ray detector 101 no longer functions normally.

[0089] Before the output of the gamma ray detector 101 becomes saturated, the high-energy gamma ray dose analyzer 152 switches the gamma ray detection device to the non-energy analysis type gamma dosimeter 151. The high-energy gamma ray dose analyzer 152 also calculates a high-energy gamma ray dose alternative value by multiplying the output of the non-energy analysis type gamma ray dosimeter 151 by a high-energy gamma ray dose conversion coefficient provided in advance.

[0090] A description will be given of a method for calculating a high-energy gamma ray dose alternative value using the high-energy gamma ray dose analysis device 152. Fig. 21 shows the relationship between the output (detector output D) from the gamma ray detector 101 and the non-energy analysis type gamma dosimeter 151 and the high-energy gamma ray dose S. Generally, when the amount of gamma rays incident on a gamma ray detector becomes excessive, the linearity of the response is lost, and the detector reaches a detection upper limit where measurement is no longer possible. For example, in Fig. 21, the detector output 101a of the gamma ray detector 101 and the detector output 151a of the non-energy analysis type gamma dosimeter 151 show curves where the linearity of the response is lost in the high range of high-energy gamma ray dose S. For this reason, depending on the work conditions, the amount of gamma rays in the work area 109 may become high, and the detection upper limit of the gamma ray detector 101 used at the beginning of the work may be reached. The radiation monitoring system 800 is equipped with a gamma ray detector 101 and a non-energy analysis type gamma dosimeter 151 that has a higher upper detection limit than the gamma ray detector 101. With this configuration, the radiation monitoring system 800 can increase the upper limit of the monitoring range for high-energy gamma ray doses S.

[0091] Furthermore, the high-energy gamma ray dose analysis device 152 sets a response switching region 154 as a region where the responses of the gamma ray detector 101 and the non-energy analysis type gamma dosimeter 151 overlap. When the response is on an upward trend, the high-energy gamma ray dose analysis device 152 switches the source of acquisition of gamma ray information from the gamma ray detector 101 to the non-energy analysis type gamma dosimeter 151 within the response switching region 154. When the response is on a downward trend, the high-energy gamma ray dose analysis device 152 switches the source of acquisition of gamma ray information from the non-energy analysis type gamma dosimeter 151 to the gamma ray detector 101 within the response switching region 154.

[0092] In the high-energy gamma ray dose analysis device 152, a relational expression between the gamma ray detector 101 and the non-energy analysis type gamma dosimeter 151 and the high-energy gamma ray dose S is set in advance. For example, if the output of the gamma ray detector 101 is D1 and the output of the non-energy analysis type gamma dosimeter 151 is D2, the conversion expressions [S=a1×D1+b1] and [S=a2×D2+b2] are used. In situations where the gamma ray dose increases depending on the working conditions, it is assumed that the main cause of the gamma ray dose is nuclear fission. Furthermore, it is assumed that the intensity of the alternative gamma ray dose from an external neutron source is very small compared to the change in the high-energy gamma ray dose. For this reason, when calculating the inverse multiplication factor 1 / M while using the non-energy analysis type gamma dosimeter 151, the set value of the high-energy gamma ray dose S is maintained at the most recent state before switching from the gamma ray detector 101 to the non-energy analysis type gamma dosimeter 151. When switching back to the gamma ray detector 101, evaluation is performed using the original usage.

[0093] The inverse multiplication analyzer 153 has the function of the inverse multiplication analyzer 105 of the radiation monitoring system 100 of the first embodiment, as well as the function of taking in a substitute value for the high-energy gamma ray dose and calculating the inverse multiplication 1 / M.

[0094] By using the radiation monitoring system and radiation monitoring method described above, even if the ambient dose rate in the work area 109 becomes extremely high, it is possible to grasp the criticality margin even for objects containing nuclear fuel whose properties are partially unclear.

[0095] In the above-described embodiments, the gamma ray energy analyzer 102, the neutron flux analyzer 104, the inverse multiplication analyzers 105, 153, the inverse multiplication curve processors 106, 150, the work feasibility processors 132, 140, the worker communication device 133, the neutron absorber injection system 134, the gas management system output conversion processor 139, the remote access control system 143, the remote work control system 145, the work plan update system 146, the high-energy gamma ray dose prediction device 149, and the high-energy gamma ray dose analyzer 152 can each be configured using a known computing device. Although the above-described embodiments describe each of the above components as separate computing devices, they may also be implemented as functional components within a single computing device. These computing devices may include, for example, a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and the like. The CPU is an example of a calculation unit related to the radiation monitoring systems 100, 200, 300, 400, 500, 600, 700, and 800. The CPU centrally controls the operation of each unit of the radiation monitoring systems 100, 200, 300, 400, 500, 600, 700, and 800. The CPU reads out program code of software related to various processes of the systems 100, 200, 300, 400, 500, 600, 700, and 800 stored in a ROM (an example of a recording medium) and loads it into a RAM. The CPU then controls the inspection device 200 in accordance with the loaded program. Note that the device control unit 250 may include another calculation unit, such as an MPU (Micro Processing Unit), instead of a CPU. Furthermore, each arithmetic unit may have a communication interface. The communication interface is configured, for example, by a network interface card (NIC) or a modem, and establishes a connection with a communication partner device via a network such as a LAN, and executes transmission and reception of various data. Each arithmetic unit is connected to other arithmetic units via the communication interface, and transmits and receives information.

[0096] Furthermore, the present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to embodiments including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to delete part of the configuration of each embodiment, or to add or replace other configurations. [Explanation of symbols]

[0097] 100,200,300,400,500,600,700,800 Radiation monitoring system, 101 Gamma ray detector, 102 Gamma ray energy analyzer, 103 Neutron detector, 104 Neutron flux analyzer, 105,153 Inverse multiplication analyzer, 106,150 Inverse multiplication curve processor, 107 Display device, 108 Measurement object, 109 Work area, 130 Criticality prediction point, 131,155 Criticality margin, 132,140 Work readiness processor, 133 Communication device between workers, 134 Neutron absorber injection system, 135 Worker, 136 Neutron transfer duct, 137 Gas recovery duct, 138 Gas management system, 139 Gas management system output conversion processor, 141,142 Remote access device, 143 Remote access control system, 144 Remote work equipment, 145 Remote work control system, 146 Work plan update system, 147 Work manager, 148 Measurement object database, 149 High-energy gamma ray dose prediction device, 151 Non-energy analysis type gamma dosimeter, 152 High-energy gamma ray dose analysis device

Claims

1. a gamma ray detector that measures gamma rays; a gamma ray energy analyzer for analyzing gamma ray energy from the output of the gamma ray detector; a neutron detector that measures neutrons; a neutron flux analyzer for analyzing neutron flux from the output of the neutron detector; an inverse multiplication analyzer that calculates inverse multiplication data based on the high-energy gamma ray dose and the alternative gamma ray dose obtained from the gamma ray energy analyzer and the neutron flux obtained by the neutron flux analyzer; and an inverse multiplication curve processing device that calculates a critical margin from the high-energy gamma ray dose and the inverse multiplication data. Radiation monitoring system.

2. The demultiplication curve processing device calculates, as the critical margin, a difference between the latest high-energy gamma ray dose and an estimated value of the high-energy gamma ray dose at which the demultiplication becomes zero. The radiation monitoring system of claim 1 .

3. The gamma ray energy analyzer acquires the amount of high-energy gamma rays by setting a threshold value higher than the energy of gamma rays generated by a nuclear reaction between hydrogen and neutrons. The radiation monitoring system of claim 1 .

4. The gamma ray energy analysis device acquires, as the alternative gamma rays, gamma rays from an alternative gamma ray source that is an alternative to an external neutron source inside the object to be measured. The radiation monitoring system of claim 1 .

5. a gas control system that measures the radioactivity concentration in the gas in the work area; a gas management system output conversion processing device that calculates an output tolerance of the radioactivity concentration in the gas from the radioactivity concentration in the gas acquired by the gas management system and the value of the high-energy gamma ray of the critical tolerance. The radiation monitoring system of claim 1 .

6. a display device that displays the method output by the demultiplication curve processing device; The radiation monitoring system of claim 1 .

7. a remote access device equipped with the gamma ray detector and the neutron detector; The radiation monitoring system of claim 1 .

8. a non-energy analysis type gamma dosimeter that can operate at a higher gamma ray dose than the gamma ray detector; The radiation monitoring system of claim 1 .

9. The inverse multiplication analyzer switches the output of the non-energy analysis type gamma dosimeter before the gamma ray detector reaches output saturation. The radiation monitoring system of claim 8.

10. The gamma ray detector measures gamma rays originating from at least one alternative gamma ray source selected from Eu-154, Cs-137, Cs-134, Sb-125, Ce-144, Ba140 / La-140, Zr-95 / Nb-95, and Ru-106 / Rh106. The radiation monitoring system of claim 1 .

11. A gamma ray detector and a neutron detector are placed near the object to be measured, measuring radiation with the gamma ray detector and the neutron detector, and analyzing high-energy gamma ray dose and demultiplication data; Calculating the critical margin from the demultiplication prediction curve based on the high-energy gamma ray dose and the demultiplication data Radiation monitoring methods.

12. The critical margin is calculated from the difference between the latest high-energy gamma ray dose and the estimated value of the high-energy gamma ray dose at which the demultiplication factor becomes zero. The radiation monitoring method according to claim 11.

13. The amount of high-energy gamma rays is measured in accordance with changes in the measurement object and the working environment in which the measurement object is present, and the inverse multiplication factor is calculated. The radiation monitoring method according to claim 11.

14. Using the criticality margin and the control threshold value of the high-energy gamma ray dose, determine whether work in the work area is possible; If it is determined that work is not possible, a decision is made as to whether to insert neutron absorbing material into the work area. The radiation monitoring method according to claim 11.

15. Measure the radioactivity concentration in the gas in the work area, calculating an output tolerance of the radioactivity concentration in the gas from the value of the high-energy gamma ray of the critical tolerance; determining whether or not work can be performed in the work area using an output tolerance of the radioactivity concentration in the gas and a control threshold of the radioactivity concentration in the gas; If it is determined that work is not possible, a decision is made as to whether to insert neutron absorbing material into the work area. The radiation monitoring method according to claim 11.

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